Pennsylvania has recorded 693 measles cases in 2026, as vaccination rates in Allegheny County fall below the 95% threshold required to prevent community spread.

Since August 2026, Pennsylvania has faced a significant measles outbreak, with the state Department of Health confirming 693 cases across 38 counties as of September 14. The surge includes 133 hospitalizations and four deaths among unvaccinated residents. This marks a sharp increase from the 16 cases reported statewide during all of 2025, prompting health officials to urge residents to verify their vaccination status.

Vaccination Rates and Community Immunity

To effectively prevent the spread of measles, population vaccination rates must remain above 95%. However, Allegheny County reported a 91.8% kindergarten MMR vaccination rate for the 2025–26 school year, continuing a downward trend observed by the local health department for over a decade. Experts note that even minor declines in coverage can lead to large-scale outbreaks, as evidenced by the current situation affecting a majority of the state's 67 counties.

Transmission and Health Risks

Measles is a highly contagious respiratory virus that can spread through the air, with infected individuals remaining contagious for 3–5 days before symptoms appear. Viral particles can persist in a room for up to two hours after an infected person leaves. Symptoms include high fever, cough, and characteristic Koplik spots. Unvaccinated individuals face a 90% risk of infection if exposed, while those who are vaccinated or have previously had the disease face a roughly 3% risk. Beyond immediate symptoms, the disease can cause severe complications, including pneumonia in approximately 20% of cases. The virus is also known to suppress the immune system, potentially leaving survivors vulnerable to other infections for months or years. Health authorities require unvaccinated individuals exposed to the virus to quarantine for 21 days.

Access to Vaccination

The MMR vaccine is recommended by the American Academy of Pediatrics, with children advised to receive two doses by ages 4 to 6. In Pennsylvania, the vaccine is available at no cost through private insurance plans and is provided free of charge to Medicaid-insured, uninsured, or underinsured children at any of the state's 59 health centers.